The present invention relates generally to a hermetic scroll-type compressor including intermeshing fixed and orbiting scroll members and, more particularly, to such a compressor having an internal pressure relief valve to communicate discharge pressure into the intermeshed scrolls to thereby reduce overloading of the orbiting scroll member.
A typical scroll compressor comprises two facing scroll members, each having an involute wrap, wherein the respective wraps interfit to define a plurality of closed compression pockets. When one of the scroll members is orbited relative to the other, the pockets decrease in volume as they travel between a radially outer suction port and a radially inner discharge port, thereby conveying and compressing the refrigerant fluid.
It is generally believed that the scroll-type compressor could potentially offer quiet, efficient, and low-maintenance operation in a variety of refrigeration system applications. However, several design problems persist that have prevented the scroll compressor from achieving wide market acceptance and commercial success. For instance, during compressor operation, the pressure of compressed refrigerant at the interface between the scroll members tends to force the scroll members axially apart. Axial separation of the scroll members causes the closed pockets to leak at the interface between the wrap tips of one scroll member and the face surface of the opposite scroll member. Such leakage causes reduced compressor operating efficiency and, in extreme cases, can result in an inability of the compressor to operate.
In a compressor having a pressurized, or "high side", housing, discharge pressure has been used on the back side of the orbiting scroll member to create a compliance force to oppose the aforementioned separating force. This back pressure on the orbiting scroll, created with either pressurized refrigerant or oil at discharge pressure, causes the orbiting scroll to move axially toward and sealing with the fixed scroll to prevent refrigerant leaks.
At times, this loading of the orbiting scroll is too great, promoting rapid wear of the scroll wraps and faces with associated power losses. This overloading of the orbiting scroll is normally created by temporary high pressure conditions within the compressor caused by its associated refrigeration system. Excessive back pressure operating for too long of a time on the orbiting scroll member deforms the shape of the scrolls along with reducing the capacity of the compressor.
In some prior art compressors, having a low side or low pressure housing, a pressure relief valve is included for separating a discharge pressure cavity from the main housing cavity at suction pressure. In this type of compressor, the pressure relief valve opens to the whole suction cavity of the housing, not to the scroll set, thereby not altering the scroll set pressures instantly. The main operational feature of these prior art compressors is that they feed heated fluid at discharge pressure into the suction pressure housing to heat up and trip an overload sensor on the motor thereby halting compressor operation.
The present invention is directed to overcoming the aforementioned problems associated with scroll-type compressors, wherein it is desired to provide an internal pressure relief valve to prevent too great of an upward compliance force on the orbiting scroll member.